diff --git a/Makefile b/Makefile
index 7f3e236..3cccc4c 100644
--- a/Makefile
+++ b/Makefile
@@ -72,7 +72,7 @@ DEFS += -DSTM32F1 -D$(BOARD)
 
 # C flags
 CFLAGS += -Os -g
-CFLAGS += -std=c99 -Wpedantic -Wall -Werror -Wundef -Wextra -Wshadow -Wimplicit-function-declaration -Wredundant-decls -Wmissing-prototypes -Wstrict-prototypes
+CFLAGS += -std=c99 -Wpedantic -Wall -Werror -Wundef -Wextra -Wshadow -Wredundant-decls -Wmissing-prototypes -Wstrict-prototypes
 CFLAGS += -fno-common -ffunction-sections -fdata-sections
 CFLAGS += -I. -I$(INCLUDE_DIR) $(patsubst %,-I%,$(LIB))
 CFLAGS += $(DEFS)